SM-20 is a novel 40-kd protein whose expression in the arterial wall is restricted to smooth muscle.

We have previously reported the identification of a novel cDNA, SM-20, whose corresponding mRNA levels are regulated by growth factors in rat aortic smooth muscle cell (SMC) culture. Affinity-purified polyclonal and monoclonal antibodies were made against a 230 amino acid region of the SM-20 putative peptide expressed in the bacterial vector, pET-3b. Western blot analyses of rat and human SMC lysates detected a single protein species of approximately 40 kd. SM-20 was not detected in concentrates of the culture medium. By immunohistochemistry, SM-20 was localized to filaments in the cytoplasm of cultured SMC. Like SM-20 mRNA, levels of SM-20 protein were increased 1-3 hours after serum stimulation of rat aortic SMC. In rat tissues, SM-20 antigen was detected in abundance in smooth, cardiac, and skeletal muscle. SM-20 was also detected in some epithelial cells of the kidney, pancreas, gastrointestinal tract, and skin, but was not found in the parenchyma of the liver, spleen, or testis. In the rat arterial wall, SM-20 antigen was restricted to the SMC of the media and, after balloon arterial injury, was found most abundantly in the neointima. In human atherosclerotic coronary arteries, SM-20 antigen predominated in the SMC of the intimal plaques and was not detected in macrophages, endothelium, or adventitial cells. Thus, SM-20 encodes a protein which serves as a novel SMC-specific marker within the vessel wall.

Identification of a novel growth factor-responsive gene in vascular smooth muscle cells.

We have employed differential screening of a rat aortic smooth muscle cell cDNA library to isolate a cDNA clone, SM-20, whose nucleotide and deduced amino acid sequences are distinct from those reported previously. SM-20 encodes an mRNA of approximately 2.5-3.0 kilobase pairs which is present at low levels in quiescent vascular smooth muscle cells. SM-20 levels increase within 1 h of treatment with growth agonists (serum, platelet-derived growth factor, angiotensin II), isoproterenol, and forskolin. Cycloheximide induces high levels of SM-20 mRNA and superinduces it in the presence of serum, suggesting that the increase in SM-20 mRNA levels is not dependent on protein synthesis and is part of the primary response to growth agonists. SM-20 is expressed at high levels in tissues and cells derived from muscle (smooth, skeletal, and cardiac) and nerve (brain, PC12 cells) and is not expressed in 3T3 fibroblasts or rat 6 fibroblasts. SM-20 encodes a new member of the immediate early gene family and is unusual in that it is expressed in vascular smooth muscle, but not in fibroblasts.

Pulmonary microvascular leakage after microembolization and hemodilution.

This study examined the role of colloids versus crystalloids in pulmonary edema associated with the increased pulmonary microvascular permeability secondary to thrombin-induced pulmonary microembolism. Each of 23 healthy dogs received an intravenous injection of thrombin and a fibrinolysis inhibitor, which induced a microembolic state with increased (fivefold) pulmonary lymphatic flow and a lymph/plasma (L/P) protein ratio typical of a permeability change. Seven dogs received no treatment, eight received 15 ml/kg 10% dextran 40 (D40), and eight received 60 ml/kg Ringer's lactate solution (RL). Pulmonary water was measured serially by thermal conductivity and terminally by wet/dry weights. This preparation produced significant hemolysis; however, L/P ratios of hemoglobin approached unity in all groups. Initially there was hemoconcentration, which was reversed by RL and even more so by D40. Both D40 and RL temporarily raised the pulmonary artery and pulmonary artery wedge pressures to 15 mm Hg; D40 more than doubled the cardiac output of control or RL subjects--this was associated with a reduced pulmonary arteriolar resistance (P less than 0.05). In the early stage PaO2 was better maintained with D40 (P less than 0.02). Lymph flow increased and was comparable in all groups, as were lung water and lung weight, which tripled in all three groups. Results of this study indicated that in the presence of a pulmonary microvascular leak, colloids in doses that produced comparable microvascular pressures did not increase lung water and did not accumulate in the pulmonary interstitium. Colloids were superior to crystalloids in maintaining cardiac output, pulmonary vascular resistance, and oxygen tension in the early period after microembolism.U

Lung thermal volume as an indicator of pulmonary extravascular water.

Double-indicator dilution methods can be used for measurement of lung water. The thermal conductivity method is based on heat as a diffusible and conductivity as a non-diffusible indicator. In the present study we correlated lung thermal volume with gravimetrical measurement of extravascular lung water after thrombin-induced microembolization in dog lungs. The embolization was accompanied by significantly increased vascular permeability and accumulation of interstitial water. Under these conditions there was a close correlation between the two methods of measuring lung water (r = 0.78, p less than 0.01).

Studies on the pulmonary capillary permeability after induced microembolism.

Pulmonary microembolization was induced by infusion of thrombin during inhibition of the fibrinolytic system. After embolization cardiac output decreased, pulmonary vascular resistance and pulmonary arterial pressure increased. There was a transient decrease in PaO2. Immediately after embolization there was an increased permeability indicated by tremendous increase in lymph flow with a constant lymph/plasma protein ratio. The lymph/plasma ratio for hemoglobin and for FITC-Dextran (mw 150 000) also increased indicating leakage of large molecules. The increased permeability was accompanied by a significant increase in extra-vascular lung-water as measured both with the thermal conductivity and the dry/wet weight method.

Sialic acid-depleted red cells following acute myocardial infarction.

A reduction of red cell SA in patients following acute myocardial infarction is reported and the effects of SA-depleted red cells on cardiac index and alveolar capillary blood flow in the dog are described. The mean red cell SA in 26 patients following acute myocardial infarction was 0.021 +/- 0.001 compared with a mean of 0.031 +/- 0.002 mumol./0.1 ml RBC in 12 normal subjects (p less than 0.01). In five dogs injected with neuraminidase, an enzyme which removes SA from the red cell membrane, a 43% decrease in mean cardiac index from 2.3 +/- 0.22 to 1.3 +/- 0.16 (p less than 0.01) occurred. In films of the pulmonary microcircuation the mean widths of typical alveolar capillary beds decreased 42.6% +/- 5% (p less than 0.01). In three other dogs, autotransfusion with SA-depleted stored blood resulted in a 25% decrease in mean cardiac index from 2.0 +/- 0.21 to 1.5 +/- 0.21 (p less than 0.2), and a 21.7% +/- 0.9% (p less than 0.01) decrease in mean widths of typical alveolar capillary beds. We conclude that a reduction of red cell SA follows acute myocardial infarction and that SA-depleted red cells decrease cardiac index and alveolar capillary blood flow in the dogs.

The effect of smoke inhalation on pulmonary surfactant.

This paper details efforts to define the primary pathophysiology of acute smoke inhalation without the variables of infection, burns, or fluid resuscitation. A standard dose of smoke (wood and kerosene) was delivered at 37 C to mongrel dogs. The parameters studied included blood gases, carboxyhemoglobin, pulmonary and systemic hemodynamics, respiratory mechanics, surface tension area curves as an indication of surfactant activity, and in vivo photomicroscopy. The FiO2 of the smoke was 17 volumes per cent; the carbon monoxide 17,000 ppm. Immediately following smoke exposure, dense, nonsegmental atelectasis developed. Hemodynamic changes were insignificant, but the PaO2 fell to 49 mmHg; the right to left shunt rose from 5 to 41%. Surfactant reduction was significant: enough to cause an increase in the minimum surface tension from 7 to 22 dynes/cm. This surfactant loss may explain the atelectasis seen and the marked instability of subpleural alveolar walls. The data collected are consistent and support the acute inactivation of surfactant as one of the primary pathophysiologic events in smoke inhalation. The clinical correlation is good; surfactant loss may explain why victims of smoke inhalation are so vulnerable to fluid administration if they have thermal burns as well effectiveness of medical devices.

Post-traumatic respiratory distress syndrome.

During the past two decades there has been recognition of the role of acute respiratory failure in the deaths of patients with shock from any cause. Leaky capillaries are the common pathophysiologic event. The pulmonary capillary bed is affected by the toxic action of vasoactive substances, gastric aspirates, and fat embolism; by the obstructive action of platelet, fibrin, and leukocyte clots; and by changes in the balance between perfusion pressures and oncotic pressures. This is complicated by increases in pulmonary vascular pressures from associated heart disease or overenthusiastic replacement of blood volume. The early treatment of the shock state, early intubation and ventilation, and the use of agents designed to improve capillary integrity have led to a significant reduction in mortality from this common problem.

Prevention of pulmonary insufficiency through prophylactic use of PEEP and rapid respiratory rates.

This study evaluated the effectiveness of prophylactic positive end-expiratory pressure (PEEP) rapid respiratory rates (RRR), and high tidal volume (HTV) in prevention of congestive atelectasis. Measurements of pulmonary hemodynamics, mechanics, gas exchange, functional residual capacity (FRC), pathology, and cinemicroscopy were performed in 45 anesthetized dogs subjected to hemorrhagic hypotension. Randomly, the animals received control ventilation, HTV (20 ml. per kilogram), RRR (32 breaths per minute), or PEEP (5 cm. of water). Carbon dioxide was added as needed to maintain normocapnia. Control and HTV animals showed characteristic changes of congestive atelectasis (capillary congestion, stasis, interstitial edema, periarterial hemorrhage, alveolar edema, and hemorrhage). These microscopic and cinemicroscopic changes were prevented by PEEP and RRR and correlated with decreased physiological shunting (PEEP 10 percent, RRR 13 percent, HTV 22 percent; p less than 0.01) in the postshock phase. PEEP increased FRC by 40 percent (p less than 0.02) and reduced the pulmonary artery--small pulmonary vein gradient (PA-SPV), suggesting a direct effect on the capillary bed. RRR did not affect FRC but minimized the SPV-LA gradient. This effect on the pulmonary venules theoretically could be mediated by stimulating lymphatic flow, thereby decreasing interstitial edema. Thus PEEP and RRR are beneficial when used prophylactically but may work by widely differing mechanisms.

The role of carbon dioxide in the development of pulmonary insufficiency.

The effects of carbon dioxide (PCO2 = 40 versus PCO2 = 20) on pulmonary function changes during 2 hours of hemorrhagic hypotension followed by resuscitation are evaluated in 21 dogs. Pulmonary hemodynamics, mechanics, gas exchange, functional residual capacity, and morphology are studied. In the preshock period, hypocapnia is associated with a decreased cardiac output, increased dead space, and increased alveolar-arterial (A-a) gradiant (room air). During the period of hypotension, all parameters in both groups changed similarly. After resuscitation, the A-a gradients in the two groups further widened. Following the return to control levels of normocapnia in all animals, the group which had been hypocapnic during the hypotensive episode continued to show increased shunting (20 versus 13 percent, p less than 0.05). These results correlated well with cinemicroscopic findings, which showed the normocapnic group to have less interstitial edema and better capillary flow.

Hemodynamic and functional changes in xenogenic, perfused, isolated lungs.

Hyperacute pulmonary rejection was reproduced by perfusion of the isolated lung with heparinized heterologous blood. The cat lung was perfused with dog venous blood at a pressure of 30 mm. Hg. Pulmonary hemodynamic and functional studies showed that blood flow decreased to 14 per cent of the control and pulmonary vascular resistance increased sevenfold. Dynamic pulmonary compliance decreased only slightly to 83 per cent at 15 minutes, but normal pH, PO2, and PCO2 were maintained in the pulmonary venous blood even 15 minutes after the start of perfusion, because perfusion was decreased to a greater extent than ventilation.

Cinemicroscopy of hyperacute pulmonary rejection.

Rejection processes were studied in xenografts and allotransplants of cat or dog lungs to dogs. Cinemicroscopy of the microcirculation in untreated animals showed almost immediate sludging, cellular aggregation, reduced vascular caliber, diminished blood flow, and rapid development of perivascular edema. The principal mechanisms of the extremely rapid xenograft rejection include capillary and arteriolar obstruction due to cellular aggregation. Pretreatment with heparin was virtually valueless, while methylprednisolone offered temporary protection.

The respiratory distress syndrome.

Acute RDS is a clinical and pathologic phenomenon with many causes. Some of the pulmonary problems are iatrogenic, resulting from the overuse of blood, crystalloids, oxygen, vasopressors, sedation, and immobility. Some are related to the blast effects of injuries at sites distant from the thorax. Other causative factors are metabolic, secondary to diminished peripheral perfusion. The pulmonary capillary bed is a principal target organ in shock--affected by the toxic action of vasoactive substances, gastric aspirates, and fat; by the obstructive action of platelet, fibrin, and leukocyte clots; and by changes in balance between perfusion pressures and oncotic pressures. The rationale of prevention and therapy presented here has resulted (except in those patients with prolonged sepsis) in almost complete disappearance of RDS as a cause of death in our institution.